Degree Type

Dissertation

Date of Award

2004

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

James H. Espenson

Abstract

In this work, methyltrioxorhenium (MTO) was found to be an active catalyst for two reactions: one is the reduction of hydronium ions by Euaq 2+ to evolve H2; the other is reduction of perchlorate ions to chloride ions by Euaq2+ or Craq 2+ in acidic solution. Kinetic studies were carried out and reaction mechanisms were proposed to agree with all the experimental data. In the hydrogen evolution reaction, a rhenium(V) hydride complex was postulated in the scheme to generate H2 by a proton-hydride reaction. Under similar conditions, Cr2+ ions do not evolve H2, despite E° Cr ~ E°Eu. In addition, no H2 formation were observed in the presence of perchlorate ions because the reaction between methyldioxorhenium (MDO) and perchlorate ions has a much faster rate than that of hydrogen evolution.;A six-coordinate rhenium(V) compound MeReO(edt)(bpym) was prepared, characterized, and investigated for oxygen atom transfer reactions between picoline N-oxide and triarylphosphines. We found it is a good catalyst for the reaction, even though it is less active than those five-coordinate rhenium(V) dithiolato compounds. The kinetics showed that the reaction has a first-order dependence on both rhenium and picoline N-oxide. Triarylphosphines were found to inhibit the reaction, and those phosphines with more electron-donating groups in para positions had slower reaction rates. This study proves a hypothesis: there should be a steric requirement for the potential catalyst in the oxygen transfer reactions, which is the necessary existence of an open coordination site on rhenium center.;In the last chapter, we studied three different types of reactions of phthalimide N-oxyl radicals (PINO·) and N-hydroxylphthalimide (NHPI) derivatives. First, the self-decomposition of PING· follows second-order kinetics. However, when excess of 4-Me-NHPI are used in the system, it was found that H-atom abstraction competes with the self-decomposition of 4-Me-PINO·. Second, the hydrogen atom self-exchange reactions between PINO· and substituted NHPI were found to follow H-atom transfer rather than the stepwise electron-proton transfer pathway. Last, the investigations of hydrogen abstraction from para-xylene and toluene by PINO· show large kinetic isotope effects, with the reaction becoming slower when the ring substituent on PINO· is more electron donating.

DOI

https://doi.org/10.31274/rtd-180813-11404

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu

Copyright Owner

Yang Cai

Language

en

Proquest ID

AAI3158318

File Format

application/pdf

File Size

127 pages

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